Summary
We propose to adopt a new airworthiness directive (AD) for the Bell Helicopter Textron Canada Limited (BHTC) Model 407 helicopters. This proposed AD is prompted by a review of the tailboom-attachment installation, which revealed that the torque value of the bolts specified in the BHTC Model 407 Maintenance Manual and applied during manufacturing was incorrect and exceeded the torque range recommended for the bolts. This proposed AD would require you to replace tailboom- attachment hardware (attachment hardware), and perform initial and recurring determinations of the torque on the nuts of the tailboom-attachment bolts (bolts) at all four attachment locations. The actions required by this proposed AD are intended to prevent an over-torque of a bolt, bolt failure, loss of the tailboom, and subsequent loss of control of the helicopter.